Declaring Tax Returns

Here's my situation:

I've been investing through my father's bank for the past couple of years. However, the bank charges a fee of €15 each time I buy or sell a stock, which adds up to a significant amount, especially since I'm dealing with smaller investments of €100-€300 per stock. The bank justifies this fee by handling the tax return forms, so I don't have to worry about it.

My father insists that I continue investing this way, as he believes using brokerage apps would be an unnecessary hassle. I want to diversify my portfolio without relying on ETFs, but the high fees are eating into my potential returns.

My question is: How difficult is it to calculate and declare taxes on my own? Is it worth considering a different approach to investing?

I live in EU, under 18